Drilling mud systems normally involve the mixing of components of the earth in a solvent. Sometimes, the solvent is water, and sometimes it is oil comparable to diesel oil. Such a drilling mud system is normally a mixture of barites, components of the earth, which are mixed into the solvent. Roughly, they have a density of about 4.4 using water as a density of 1.0. This density or specific gravity defines the basic two component system. After use, the drilling fluid is returned to the surface. It is usually returned with a mix of cuttings which are pulverized into a wide range of particle sizes. The particles are removed and the drilling fluid is recirculated. Throughout the project, it is necessary to clean up the drilling fluid. The drilling fluid is three components. The major component in terms of volume is the solvent. Again, typically, it is water or diesel oil. The third component that is added all the time through the drilling process is particles from the drilling process. These can be relatively large. The third component is derived from the components of the earth, typically, sand or shale, and these constitute a significant portion of the returned drilling fluid. In fact, they are the portion that corrupts or spoils the drilling fluid.
It is important in determining a mud system for a given well that the weight of the mud must be controlled to a specified elevated level. The weight of the mud is increased from 8 pounds per gallon (the baseline value associated with pure water) up to 12, perhaps 14 and even 16 pounds. This gain in weight is achieved by adding barites. During use, the weight must be stabilized. Otherwise, the mud is not useful. Sometimes it is passed through degassers, desanders, shale shakers, and other equipment to clean the mud during use. Whatever the circumstance, the drilling fluid cuttings are ultimately a waste product from the drilling process that is difficult to dispose of. Cuttings may include components which are removed, if possible, and the present disclosure sets forth an approach for doing that. It is not uncommon for a mud system to involve 1,000 or more barrels. It is not uncommon to have as much as $1 million of mud flowing in the system depending on the components in it. In terms of cleaning the mud system and breaking it down into easily segregated ingredients, the best that has been done in the past has primarily been screening of the heavy particles which derive from the drilling process itself. That is a good first step, but it is not adequate.
For a more adequate approach, the cleaning of the present disclosure is the retrieval of the mud and centrifuging it into two components, one being the mud and the other being solids which are removed from it. In particular, this system works well to remove cuttings in the drilling fluid and to enable recovery of the solids in the drilling fluid, thereby removing waste products for continued drilling. Effectively, the expensive process of cutting disposal is significantly avoided and cuttings are converted into segregated byproducts leaving the mud recovered from it.
This disclosure is directed to an improved centrifuge which especially finds use in cleaning drilling mud. In particular, it is able to extract sand and shale in the drilling mud. The present system is summarized as an improved centrifuge having a rotating bowl which is constructed with a set of slots in it so that it has controlled leakage through the bowl. The bowl is tapered at one end to connect with an inlet line. The drilling mud introduced at that end is delivered into the bowl and is directed outwardly by a set of acceleration vanes. They force the liquid to flow to the outside, rotating on the interior of the bowl. As it flows along the bowl, the liquid is permitted to pass through a set of slots. The slots are relatively narrow so that particles above a certain size do not pass through the slots. The particles that are too large for the slots remain on the interior of the bowl and are picked up by the flites of the conveyor which is a single helix screw of about 5 to 10 turns. The flites extend outwardly to a common diameter adjacent to the bowl. At the remaining end, the flites taper inwardly to cooperate with a solid wall beach tapered end of the bowl. The beach terminates at a set of openings where the dry components are forced to the left and out of the bowl at a solids outlet. A surrounding housing includes an internal wall dividing the housing. The housing is stationary over the bowl. It includes a liquid discharge outlet at the center and a solids discharge at the end adjacent to the beach.
In one important aspect, a slotted bowl is constructed for this equipment. The bowl is not made of one piece; in this instance, the bowl is constructed of a number of segments. The segments are positioned so that they define a number of slots of common length. This unitized construction enables the bowl to be assembled with a requisite number of slots around the circle. For example, the bowl can be readily made with a selected number of slots. In the preferred embodiment, the bowl is assembled with 960 slots around the circle, the preferred bowl diameter being 36 inches. This provides an adequate slot area for large production. The length of the bowl is incremental. To assure that centrifugal forces do not bow the components and thereby distort the slots between adjacent pieces, they are relatively short. Arbitrarily assigning a length of about 5 inches, each of the several slots is made identically to all the others, and this is replicated so that the bowl length is 5 inches or multiples thereof. By making the slot to a specified width, the preferred embodiment being approximately 0.003 inches, the slots in a 5 inch long segment provide a cross-sectional area of about 15 inches as a feed through. A 15 inch cross-sectional area is sufficient to process 100 gallons or more per minute through the centrifuge. By expanding the bowl in length, capacity can be increased to 200, 300 and so on.